I think you shouldn't need to worry about that because more and more I see there are many newbies ranked up to full member ranks, some users also have higher merits than the activities. So the sMerit distribution in this forum is still working, but we can't predict the future, maybe we will see evil sMerit or theymos start to decay someone sMerit from some period of time.
What could make it seem like merits are exhausted in the forum is when either merit sources or members with merits do not distribute merits to other users but that scenario is not possible
Why it's not possible? it's technically possible similar like people who say Bitcoin could dump to $1 due to almost no demand.